This invention relates to methods and apparatus for spraying fluids, e.g. liquids such as herbicides and pesticides, from a moving vehicle. More particularly, the invention relates to a spray device for spraying liquids from a moving aircraft in a manner which allows the operator to carefully control the spray pattern and to minimize undesired drift. If desired, the spray device can be adapted for use with land equipment. The spray device has the virtue of requiring only very simple maintenance. The invention further relates to a method of varying the swath width of a spray pattern during a spraying operation without the need for a complicated system of shutoff valves.
The problem of drift during the spraying of herbicides and pesticides is well known and is discussed in my U.S. Pat. Nos. 3,445,065 and 3,523,646. The term "drift" refers to the displacement of a portion of the spray from its intended spray pattern into undesired areas. Drift is generally caused by unpredictable winds, drafts, air turbulence, etc. Minimization of drift is a major objective in spraying operations. The powerful properties of a systemic herbicide are such that a few drops of the systemic herbicide are sufficient to kill a plant. While systemic herbicides are selective, such herbicides will attack certain economic crops, therefore, they must be applied in a carefully controlled manner. Likewise, untoward results can ensue if systemic insecticides drift into areas where it is not intended to apply them.
As discussed in the previously mentioned U.S. patents, the problem of drift is particularly acute when fine droplets are present in the spray. Generally, droplets of less than about 300 microns in diameter are considered to be undesirable from the point of view of being subject to drift. To control drift it is considered highly desirable to have spray devices which produce droplets of substantially uniform size.
U.S. Pat. Nos. 3,445,065 and 3,523,646 describe means of spraying liquids in such a manner that undesired drift is minimized.
It is disclosed in the previously mentioned patents that the problem of drift can be minimized by discharging the liquid in a laminar stream from a spray nozzle while the nozzle is moving in a direction substantially opposite the direction of spray discharge. By discharging the stream in a direction opposite the direction of movement of the nozzle the formation of small "satellite" droplets is prevented. These satellite droplets, which are formed when liquid is discharged in a laminar flow from a stationary nozzle, tend to be subject to drift in cross winds and the like.
Several spray devices are disclosed in U.S. Pat. Nos. 3,445,065 and 3,523,646 for spraying liquids in a manner which minimizes drift. All of these devices employ a series of discharge tubes which are pointed in a direction opposite the direction of movement of the nozzle during use.
All of these devices further employ some mechanism for preventing drippage from the nozzles upon shut off of the liquid supply. In one embodiment disclosed in U.S. Pat. No. 3,445,065, each of the individual discharge tubes contains a small valve which closes upon cessation of liquid pressure. Unfortunately, the large number of such valves and the small diameter of the discharge tubes creates maintenance problems, which are particularly troublesome when the device is employed in remote agricultural areas where skilled mechanics are not readily available. The numerous small valves require regular maintenance to remain in good working order. Moreover, they are relatively easily clogged by contaminants or when attempting to spray liquids which contain suspended solids.
In another embodiment, U.S. Pat. No. 3,445,065 discloses a spray device in which the discharge tubes emanate from a hollow body of airfoil configuration which contains an absorbent material such as a sponge. U.S. Pat. No. 3,523,646 discloses a similar device in which each of the discharge tubes is in fluid communication with the absorbent material by means of a capillary tube. The use of the capillary tube prevents drippage when positive pressure is removed from the liquid in the absorbent material. These capillary tubes also require periodic maintenance to ensure that they are kept clear and they are subject to clogging by contaminants or suspended solids. Likewise, the absorbent material can become contaminated and it prevents the use of liquids containing suspended solids. A further problem with this type of device is that the hollow body containing the absorbent material is a relatively large body which is located in front of the discharge tubes as the vehicle moves forward. Consequently, it can create air turbulence which is capable of breaking up the spray pattern and causing the formation of non-uniform droplet sizes which result in drift. While the hollow body is generally of an airfoil configuration to reduce turbulence, it is necessary for the operator to make frequent adjustments to the angle of the airfoil as the attitude of the vehicle (e.g. a helicopter) changes in order to keep the airfoil "in trim." When the spray device is employed on an aircraft, the presence of the hollow body in front of the discharge tubes represents a limiting factor of the maximum airspeed at which the device can be operated with reasonable assurance that air turbulence will not break up the spray and cause drift.
Another problem which exists with spray devices known in the prior art is that they generally employ discharge tubes which are arranged along a boom which is affixed to the vehicle so that the tubes are in an essentially planar configuration. The resultant spray discharge thus forms a "blanket" of spray. As this blanket settles to the ground it has the ability to compress a certain amount of air beneath it. Upon nearing the ground this compressed air is forced to move laterally, creating ground turbulence which can displace the spray laterally from its target area.
Frequently, it is desired to vary the swath width of the area being sprayed while the vehicle is in motion. For example, when spraying herbicides from an aircraft to control vegetation along a power line right-of-way, it is not uncommon for the right-of-way to suddenly narrow or widen on one or both sides. In order to allow the pilot to shut off spray nozzles on the end sections of the boom, it has been necessary to have a series of shutoff valves and associated controls in the liquid supply boom. This further complicates maintenance procedures and adds weight to the boom. Even a small amount of additional weight on the boom, which is cantilevered from the aircraft, is considered undesirable.
It is an object of the present invention to provide a spray device which will spray liquids, such as herbicides and insecticides, in droplets of essentially uniform size from a moving vehicle, such as a helicopter or airplane, so as to minimize the problem of drift.
It is another object of the invention to provide such a spray device which is constructed in such a way that it requires only very simple maintenance to keep it in good operating condition. It is a further object that the spray device should not easily become clogged by contamination and should be capable of spraying liquids containing suspended or dispersed solids without clogging.
It is another object of the invention to provide a spray device which can be operated from an aircraft at relatively high speeds without substantial loss of droplet uniformity or drift control. Moreover, it is an object to provide a spray device which can be operated from an aircraft without the need for frequent critical trim adjustments by the pilot to control the spray pattern.
It is another object of this invention to minimize the problem of ground turbulence which displaces a spray from its intended target area.
It is yet another object of the invention to provide an apparatus for spraying a fluid from a moving vehicle which allows the operator to vary the swath width of the spray pattern while the vehicle is in motion without the need for a complicated series of shutoff valves.
Other objects and advantages of the present invention will be apparent to the skilled worker in the art from the description that follows.